Diversity of and biogeographic insights into the Atlantic Eocuma (Cumacea: Peracarida)

Abstract The Gulf of Guinea is characterised by a complex hydrology and supports a high species diversity. A recent study has indicated that the area can be considered a refuge for rare taxa. Intensive sampling off the coast of Ghana (Gulf of Guinea) in 2012 on board the R/V F. Nansen resulted in the discovery of a large number of benthic invertebrates, including peracarid crustaceans. A preliminary investigation demonstrated a high diversity of the Cumacea, with 95% of the species being new to science. The most species-rich genus was Eocuma with seven species; six of them proved new to science and are described here. Additionally, the global distribution of Eocuma was analysed with the help of a phylogenetic tree based on morphological characters, Bayesian Binary Markov chain Monte Carlo biogeographic analysis and literature data. The radiation centres of the west African fauna are discussed.


Introduction
The genus Eocuma Marcusen, 1894 was erected to accommodate Eocuma hilgendrofi Marcusen, 1894 found off Japan. The genus was defined by a flattened carapace and the position of the first pereopods in ventral view, where the basal article comes to the midline (Marcusen 1894). The illustrations missing from the original description were later added by Zimmer (1903), who noticed that the position of pereopods shifts during ontogenesis. However, because a similar pereopod position was observed in a few other genera (Calman 1904), this character was discarded as a diagnostic feature for Eocuma. As the lack of unique characters made the definition of Eocuma vague, Calman (1904) transferred a few bodotriid species (i. e. Bodotria ferox (Fischer, 1872) and Cyclaspis sarsii (Kossmann, 1880)), with the carapace armed in lateral horns, to the genus. By that time, and after two new Eocuma species (E. affine and E. taprobanicum) had been discovered in the Gulf of Maanar (Indian Ocean), the genus contained five species (Fischer 1872;Kossmann 1880;Zimmer 1903;Calman 1904).
Somewhat later, Calman (1907aCalman ( , 1907b) described four species: one (E. longicorne) from the vicinity of Suez (Calman 1907a), two (E. latum and E. stelliferum) from the Gulf of Thailand (Calman 1907a), and one (E. dollfusi) from the Gulf of Biscay (Calman 1907b). Subsequently, Zimmer (1914) and Fage (1928Fage ( , 1950 published descriptions of E. agrion from Australian waters and E. calmani and E. cadenati from off western Africa, respectively. Over the next few years, knowledge on the diversity and distribution of Eocuma was significantly expanded. New species were found off the Indian coasts (Kurian 1951(Kurian , 1954 and off Japan (Gamô 1967). A survey of the South Africa fauna carried out by Day (1978) resulted in discovering three new species (Day 1978). She supplemented the generic diagnosis of Eocuma by adding several characters, e. g. the pereonite 1 always covered by the carapace, the basis of the maxilliped 3 with a dorsodistal extension, the six-articled pereopod 2, and the onearticled endopod of the uropod (Day 1978). Following that new and restricted definition of Eocuma, seven species were described from the tropical Indian Ocean (Kurian & Radha Devi 1983;Mühlenhardt-Siegel 1996;Petrescu 1998Petrescu , 2003Patel et al. 2003;Corbera et al. 2005). In addition, Haye (2007) synonymised Mossambicuma Day, 1978 with Eocuma, whereby the genus was complemented by M. elongatum Day, 1978and M. victoriae Mühlenhardt-Siegel, 2003. Recently, Kim et al. (2020 described a species (E. obriculatum) from the Korean waters.
At present, Eocuma is represented by 32 nominal species, which makes it the fourth most speciose bodotriid cumacean genus. However, despite the relatively long history of taxonomic studies on the genus, the knowledge of its diversity and distribution patterns is still far from complete.
The Gulf of Guinea is located off the west coast of equatorial Africa. It is characterised by a complex hydrology driven by several currents, i.e. the Guinea, Benguela and South Equatorial Counter Currents (Ukwe et al. 2006). In the northern part, environmental conditions are shaped by upwelling, while the southern part is strongly affected by nutrient input from land drainage and river runoff (mainly the Volta River) (Ukwe et al. 2006). This unique environmental setting is considered to support a high biodiversity in the region, recognised in the Marine Ecoregions of the World (MEOW) as a discrete ecoregion (Spalding et al. 2007).
Recent surveys of the Gulf of Guinea within the framework of the Oil for Development (OfD) Program (Annual Report 2019) under the aegis of the Food and Agriculture Organization of the United Nations (FAO) resulted in the discovery of a high biodiversity of benthic crustaceans, including peracarids (Jakiel et al. 2015;Stępień et al. 2021;Jóźwiak et al. 2022). For example, 95% of morphospecies in only one peracarid order, the Cumacea, collected off the Ghana coast proved new to science (Stępień et al. 2021). The genus Eocuma, represented by seven species, appeared to be the most diverse, and E. calmani Fage, 1928 was formally described.
This study is aimed at a taxonomic examination of Eocuma, an abundant and diverse cumacean genus identified in the benthic collection from the Gulf of Guinea. Six species new to science are described, and the worldwide distribution of Eocuma is analysed. Based on the current knowledge, we discuss the unique nature of the west African shallow-water fauna and its hypothetical dispersal routes.

Sampling
The material was collected with a Van Veen grab (0.1 m 2 ) in October-November 2012 on board R/V Fridtjof Nansen. The sampling process was described by Pabis et al. (2020). The samples were sieved through a 0.3 mm mesh size sieve and preserved in 4% formaldehyde solution. Table I provides the location of the sampling sites.

Morphological studies and taxonomic description
Chemically sharpened tungsten needles were used for dissection of the individuals selected for detailed morphological analyses. The dissected appendages were placed on a microscopic slide in a drop of glycerine and closed with a coverslip. Drawings were prepared using a light microscope (Nikon Eclipse 50i) equipped with a camera lucida. Publication-quality illustrations were prepared using a digital tablet and Adobe Illustrator software (Coleman 2003). The morphological description follows Jakiel et al. (2019), with "BL" standing for body length, "Nx" replacing "N times as long as" and "N L:W" replacing "N times as long as wide". The type material was deposited at the University Museum of Bergen (Norway).

Phylogenetic analysis
A phylogenetic analysis was performed to investigate phylogenetic relationships between the Eocuma species. A matrix with 47 morphological characters and 33 Eocuma species including the newly described six was compiled. Thirty-two species were classified as an ingroup. Six species (E. affine Calman, 1904, E. agrion Zimmer, 1914E. bacescui Petrescu, 2003;E. dimorphum Fage, 1928;E. hilgendorfi Marcusen, 1894;E. muradianae Petrescu, 1998) were excluded from the analysis because of their poor descriptions which included only the general appearance of the body and no details on either the pereopods or mouthparts. Both females and males were analysed; sexually dimorphic characters were considered separately for males and females. Based on the systematics and phylogeny of the family Bodotriidae (Haye 2007), Upselapsis caparti (Fage, 1951) was selected as an outgroup.

Biogeographical analysis
The distribution range of Eocuma was divided into six areas according to the realms proposed by Spalding et al. (2007) North Atlantic (TNA), and (F) Central Indo-Pacific (CIP). Should a species be recorded in two or more realms, only the type locality is considered (to avoid a possible misidentification). To analyse the possible ancestral range, the Bayesian Binary Markov chain Monte Carlo analysis (BBM) using the consensus phylogenetic tree was employed. BMM suggests possible ancestral ranges at each node and calculates probabilities at each ancestral range at the node (Joy et al. 2016). BMM was conducted with the Reconstruct Ancestral State in Phylogenies (RASP; Yu et al. 2015). The MCMC chains were run simultaneously for 50,000 generations. The state was sampled every 100 generations. The fixed Jukes-Cantor was used for BBM with the null root distribution. The maximum number of areas was six.

Phylogenetic analysis
Heuristic searches resulted in four most parsimonious trees from which the consensus tree was developed ( Figure 1) (length 152 steps, CI = 0.33, RI = 0.56). The RBS did not produce a significant value; the few branches that produced RBS > 0.5 are shown in Figure 1.
Clade 61 separates two species, E. victoriae and E. elongatum, from the remaining Eocuma species. The clade is supported by the following synapomorphies: maxilliped 3 ischium 3x merus, peropod 1 propodus longer than dactylus (at least 2x), the presence of relatively elongated siphon, and RBS equal to 0.5. Clade 60 contains the other Eocuma species studied and was distinguished due to: carapace with 1.5 L:W or less, the presence of a projection on the basis of pereopod 1, and Maxilliped 3 ischium 2x merus or shorter. Three species (E. foveolatum, E. dollfusi and E. nansenae) failed to group with clade 60, but formed a cascade of branches (clades 60, 59 and 58). Eocuma foveolatum was distinguished due to the lack of horns and the proportion of articles of the second and third pereopods: pereopod 2 merus 1.2x carpus and pereopod 3 merus 0.8x carpus. Eocuma dollfusi was separated due to: pereopod 1 basis shorter than the length of ischium, merus, carpus, propodus and dactylus combined, and pereopod 1 dactylus shorter than propodus. Eocuma nansenae was separated due to a combination of the following characters: pseudorostrum situated on the horn level and a narrow ocular lobe.
The The second main lineage (clade 47) contains species (E. amakusense, E. cadenati, E. calmani, E. carinocurvum, E. cochlear, E. guinean, E. kempi, E. latum, E. longicorne, E. mandeli, E. orbiculatum, E. rosae, E. sarsii, E. stelliferum, E. striatum, E. taprobanicum and E. winri) with the carapace tapering towards the posterior and a distinct antennal notch. Although grouped with clade 47, E. sarsii is associated with a separate branch because of a relatively short uropod peduncle (0.25x rami), the presence of one pair of horns which are 2 L:W, and pseudorostrum situated at the level of the horns.

Biogeographical analysis
Results of the BBM analysis show the genus to be dispersed in 19 areas ( Figure 2). The ancestral state is SA, with an 82% probability for clade 61, grouping E. victoriae and E. elongatum. The same ancestral state, with a probability of 88%, is proposed for clade 60 grouping the remaining Eocuma species. TNA is revealed as the ancestral state for clade 59 (E. dollfusi). A single dispersal, to the tropical part of the Atlantic (TA), is indicated for the next clade (58, with E. diaboliceus).
WIP is proposed as the ancestral state (with 63% probability) for clade 57 which divides Eocuma into two main lineages. Alternative ancestral states include TNP (13% probability) and TA (12%).
The ancestral state of the first main lineage (clade 56) remains unresolved, with three areas, TNP, WIP and TA, showing similar probabilities (32%, 29% and 26%, respectively). WIP is indicated as the ancestral state (98% probability) for the second main lineage (clade 47). Within clade 47, a single dispersion to TA (clades 36 and 39) as well as to CIP and TNP (clade 40) is observed.
Antenna not observed. Left mandible (Figure 4(b)) with row of 10 plumose setae, incisor with four teeth, lacinia mobilis with three teeth.
Right mandible (Figure 4(c)) with a row of 11 plumose setae, incisor with three teeth.
Maxilliped 1 (Figure 4(e)) basis stout, with simple seta on medial surface, with bunch of setules on outer distal corner, and with three plumose setae on inner margin; endite with four plumose terminal setae (one with broad basis), with two plumose setae on medial surface and two hook setae on inner margin; merus 0.5x carpus, with no setae; carpus 1.4x propodus, with six flattened setae accompanied by simple seta along inner margin, with numerous setae on medial surface, and with plumose seta on outer distal corner; propodus 2.5x dactylus with four simple terminal setae and two subterminal setae; dactylus terminated with two simple setae.
Maxilliped 2 (Figure 4(f)) basis as long as remaining articles combined, with two plumose setae on inner distal corner, and with short simple setae along outer margin; ischium short, with no setae; merus as long as carpus, with plumose setae on medial surface; carpus 0.8x propodus, with five plumose setae along inner margin; propodus 2.1x dactylus, with five plumose setae along inner margin; dactylus 0.4x propodus, with four simple terminal setae.
Maxilliped 3 (Figure 4(g)) basis 0.6x remaining articles combined, with crenulation along inner margin in distal half, distal prolongation reaching articulation of ischium and merus, with a row of five plumose setae along inner margin, a row of six simple setae along outer margin, and with three simple distal setae; ischium 0.4x merus, with four plumose setae along inner margin; merus 1.4 L:W, as long as carpus, with four plumose setae along inner margin; carpus 2.0 L:W, as long as propodus, with no setae; propodus 2.1 L:W, as long as dactylus, with two plumose setae at medial surface; dactylus with four sharp teeth along inner margin, minute seta on outer margin in proximal half, and with five simple terminal setae. Exopod as long as basis.
Pereopod 3 ( Figure 5(c)) basis 1.1x remaining articles combined, with simple seta and plumose seta on lateral margin, and with two simple distal setae; ischium 0.6x merus, with simple distal seta; merus as long as carpus, with simple setae at medial surface; carpus 1.5x propodus, with simple seta on lateral margin, and with two simple setae (one long, one short), and one bifurcated distal seta; propodus 3.4x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta. Pereopod 4 ( Figure 5(d)) basis as long as remaining articles combined, with three simple setae in proximal half, and with simple seta subdistally; ischium 0.6x merus, with simple distal seta; merus 0.8x carpus, with simple seta on medial surface; carpus 1.5x propodus, with two simple setae on medial surface, and with two simple setae (one long, one short), and one bifurcated distal seta;

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A. Stępień et al. propodus 3.5x dactylus, with bifurcated distal seta; dactylus terminated with one thin seta and one strong seta. Pereopod 5 ( Figure 5(e)) basis 0.7x remaining articles combined, with simple seta on medial surface, and simple distal seta; ischium 0.6x merus, with simple distal seta; merus 0.8x carpus, with two simple setae; carpus 1.6x propodus, with two simple setae on medial surface, and with two simple setae (one long, one short), and one bifurcated distal seta; propodus 3.5x dactylus, with bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Uropod ( Figure 5(f)) peduncle about 0.4x pleotelson, with three plumose setae along lateral margin. Endopod one-articulated, 3.2x peduncle, with row of seven plumose setae along inner margin, and row of seven short simple setae along outer margin, terminated with setulose seta. Exopod two-articulated, subequal to endopod; article 1 with two plumose setae on outer margin; article 2 with two rows of numerous setae on outer margin: first row of long plumose setae, second row of short simple setae, terminated with two stout setulose setae.

Remarks
Antennule (Figure 7(a)) peduncle tri-articulated. Article 1 widest, with parallel margins, and with two simple setae along lateral margin. Article 2 2.2 L:W, 0.7x article 3, with seta on inner and seta on outer margin. Article 3 3 L:W, with simple and penicillate distal setae. Main flagellum two-articulated, article 2 tipped with two long simple setae, one aesthetasc and one penicillate seta. Accessory flagellum minute, tipped with two penicillate and simple setae.
Antenna not observed. Left mandible (Figure 7(b)) with a row of eight plumose setae, incisor with four teeth, lacinia mobilis with three teeth.
Right mandible (Figure 7(c)) with a row of nine plumose setae, incisor with blunt tooth.
Maxilla (Figure 7(d)) outer endite with 11 spines terminally, two simple subterminal setae on outer margin, and three simple subterminal setae on inner margin. Inner endite with four stout, plumose terminal setae and numerous thin setae along lateral margin.
Maxillula (Figure 7(e)) broad endite with row of 16 subterminal setae, and with a row of 16 simple setae and one plumose terminal seta. Outer endite with five plumose terminal setae and two simple subterminal setae. Inner endite with six plumose terminal setae. Maxilliped1 (Figure 7(f)) basis stout, with six simple setae on medial surface, a bunch of setules on outer distal corner, and with seta on inner distal corner; endite with four stout plumose terminal setae and with two setae on medial surface; merus 0.3x carpus, with two setae on inner distal corner and with two setae along outer margin; carpus 1.2x propodus, with six flattened setae along inner margin, with numerous setae on medial surface, and with long plumose setae on outer distal corner; propodus 1.5x dactylus, with nine plumose setae along inner margin, and with seta on outer distal corner; dactylus 0.6x propodus, with two terminal setae and with three subterminal plumose setae.
Maxilliped2 (Figure 7(g)) basis 0.8x remaining articles combined, with one simple and two distal plumose setae and with three simple setae on outer 1060 A. Stępień et al. margin; ischium short, with no setae; merus 0.4x carpus, with plumose distal setae; carpus 1.3x propodus, with five plumose setae along inner margin; propodus 2x dactylus, with six setae along inner margin, with plumose setae on medial surface, and with plumose seta on outer distal corner; dactylus with five plumose terminal setae. Maxilliped3 (Figure 7(h)) basis stout, 0.5x remaining articles combined, with row of teeth along inner margin, and with row of six plumose setae on medial surface, distal prolongation reaching articulation of ischium and merus, with a row of eight plumose setae along distal and inner margin; ischium subequal to merus, with six plumose setae along inner margin; merus 1.2 L:W, 0.8x carpus, with six plumose setae along inner margin and with two simple setae on outer distal corner; carpus 1.4 L:W, similar in length to propodus, with two simple setae at midlength of inner margin, and with simple seta on outer distal corner; propodus 1.5 L: W, 1.2x dactylus, with two simple setae at midlength of inner margin, and with simple seta on outer distal corner; dactylus 0.8x propodus, with three simple terminal setae and two subterminal setae and with row of four short setae along inner margin. Exopod shorter than basis. Pereopod1 (Figure 8(a)) basis 0.8x remaining articles combined, proximal part wider than distal, with nine plumose setae medially, and with plumose seta on distal corner; ischium 0.4x merus, with short simple seta laterally; merus 0.8x carpus, with five plumose setae laterally; carpus 0.8x
Pereopod4 (Figure 8(d)) basis 0.8x remaining articles combined, with five simple setae and one penicillate seta laterally; ischium 0.7x merus, with simple setae subdistally; merus 0.8x carpus, with simple seta laterally; carpus 1.5x propodus, with penicillate seta laterally on proximal half, and with one simple seta and one bifurcated seta on distal corner; propodus 3.2x dactylus, with strong distal seta; dactylus terminated with one thin seta and one strong seta.
Pereopod5 (Figure 8(e)) basis 0.5x remaining articles combined, with five simple setae and one penicillate seta laterally; ischium 0.7x merus, with simple setae subdistally; merus subequal to carpus, with two simple setae laterally; carpus subequal to propodus, with simple seta laterally on proximal half, and with two setae (one broken) on distal corner; propodus 3.3x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Uropod (Figure 8(f)) peduncle 0.3x pleotelson. Endopod one-articulated, 4.5x peduncle, with a row of five penicillate setae along outer margin, and with a row of eight setae along inner margin, terminated with stout, setulose seta. Exopod twoarticulated, subequal to endopod, second article with three setae on outer margin, and crenulation on inner margin, terminated with two stout setulose setae.  (Figure 9(a)) 1.1 L:W, strongly flattened, with two pairs of horns, horns short (about as long as wide). Pseudorostral plates rounded. Antennal notch absent. Lateral carinae nearly reach the border of carapace.
Antennule (Figure 10(a)) peduncle tri-articulated. Article 1 trapezoidal, 3.1 L:W, 2.7x article 2, with two penicillate distal setae, and with numerous setae on lateral surface; article 2 0.6x article 3, with two penicillate distal setae; article 3 with short simple seta in proximal half, and with two penicillate setae and simple distal seta. Main flagellum two-articulated, article 2 tipped with aesthetasc and two simple
Antenna not observed. Left mandible (Figure 10(b)) with a row of 11 plumose setae, incisor with three teeth, lacinia mobilis with three teeth.
Maxilla outer endite (Figure 10(d)) with 12 spines terminally, four bunches of simple subterminal setae and plumose seta on inner margin. Inner endite (Figure 10(d')) with three plumose setae and three stout simple terminal setae, and four simple setae on outer margin.
Maxillula (Figure 10(e)) broad endite with a row of 20 subterminal setae, and with a row of 21 simple setae and two plumose terminal setae. Outer endite with five plumose terminal setae, and two simple subterminal setae. Inner endite with four plumose and one simple terminal seta.
Maxilliped 1 (Figure 10(f)) basis stout, endite with five plumose setae along distal margin, and with a row of seven setae along inner margin; merus 0.7x carpus, with two plumose setae on inner distal corner, and two simple setae on both lateral margins; carpus 1.3x propodus, with six flattened setae along inner margin, with numerous setae on medial surface, and with long plumose seta on outer distal corner; propodus 2x dactylus, with two rows of simple setae along inner margin, and two simple setae on inner margin; dactylus with two terminal setae and two subterminal short setae.
Maxilliped 2 (Figure 10(g)) basis as long as remaining articles combined, with minute setae on outer distal corner, and with two long simple setae on inner distal corner; ischium short, with no setae; merus as long as carpus, with plumose seta on inner distal corner, and numerous short setae along outer margin; carpus as long as propodus, with five plumose setae along inner margin, and short seta on outer margin; propodus 1.9x dactylus, with two rows of eight setae along inner margin, with seta on medial surface, and with long, simple seta on outer distal corner; dactylus with four simple terminal setae, with seta at medial surface, and with minute setae along inner margin.
Maxilliped 3 (Figure 10(h)) basis stout, 0.7x remaining articles combined, with long plumose seta on inner distal corner, and with simple distal seta, distal prolongation reaching articulation of merus and carpus, with a row of plumose setae along inner margin, whole surface of basis covered with minute setae; ischium as long as merus, with five plumose setae along inner margin, and with minute setae on whole surface; merus 1.3 L:W, 1.1x carpus, with three plumose setae along inner margin, and with minute setae on whole surface; carpus 1.3 L:W, as long as propodus, with plumose seta on inner distal corner, and simple seta on outer distal corner; propodus 2.3 L:W, as long as dactylus, with simple seta on inner margin, simple seta on outer distal corner, and with minute setae on medial surface distally; dactylus with two simple terminal setae, and two subterminal simple setae. Exopod shorter than basis. Pereopod 1 (Figure 11(a)) basis 0.5x remaining articles combined, with small teeth and simple setae on distal corner, and with minute setae on whole surface; ischium 0.3x merus, with no setae; merus 0.3x carpus, with small setae on medial surface; carpus as long as propodus, with six lateral setae and one distal seta; propodus 1.2x dactylus, with three short setae on medial surface, and with three long distal setae; dactylus with three simple setae laterally, with four setae (three simple, one plumose) terminally, and with two simple subterminal setae. Exopod shorter than basis. Pereopod 2 (Figure 11(b)) basis 0.5x remining articles combined, with plumose setae and two simple lateral setae; ischium fused with basis; merus 1.2x carpus, with spine on distal corner; carpus 0.7x propodus, with two simple distal setae; propodus 0.7x dactylus, with no setae; dactylus 3.1 L:W, with two lateral setae laterally and four terminal setae.
Pereopod 3 (Figure 11(c)) basis 0.8x remaining articles combined, with long plumose setae and five short lateral setae, and with simple setae on distal corner; ischium 0.4x merus, with short seta on medial surface, and with long, simple seta on distal corner; merus 0.8x carpus, with two simple lateral setae, carpus 1.6x propodus, with three simple lateral setae, and with two setae (one simple, one bifurcated) on distal corner; propodus 2.7x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Pereopod 4 (Figure 11(d)) basis 0.7x remaining articles combined, with two long simple setae, and seven short simple setae on lateral margin, and with long simple seta on distal corner; ischium 0.4x merus, with simple seta on distal corner; merus 1.2x carpus, with two lateral setae, and with two setae (one simple, one bifurcated) on distal corner; propodus 2.6x dactylus, with strong bifurcated distal seta; dactylus terminated with two thin setae and one strong seta.

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A. Stępień et al. 0.5x merus, with two simple setae on distal corner; merus 1.2x carpus, with simple seta laterally; carpus 1.3x propodus, with two simple lateral setae, and with bifurcated seta on distal corner; propodus 2.6x dactylus, with strong bifurcated distal seta; dactylus terminated with two thin setae and one strong seta. Uropod (Figure 11(f)) peduncle about 0.5x pleotelson, with two setae on lateral margin. Endopod one-articulated, 4.5x peduncle, with a row of seven setae along lateral margin and bifurcated spine on lateral margin in distal half, terminated with setulose seta. Exopod two-articulated, subequal to endopod, article2 with row of seven setae along lateral margin, terminated with two stout setulose setae.
Distribution. The Gulf of Guinea, off the coast of Ghana, Eastern Atlantic; depth 20-50 m.
Remarks. Due to the dorsoventrally flattened body and the presence of two pairs of horns, one dorsolateral and one lateral, the new species shows similarities to E. amakusense, E. cadenati, E. carinocurvum, E. hilgendorfi, E. latum, E. stelliferum, E. striatum, E. taprobanicum and E. winri. However, the new species can be distinguished from them by a combination of the following features: carapace slightly narrowing from the anterior to the posterior part, proportion of pereopod1: basis 0.5x remaining articles combined, carpus similar to propodus and dactylus 0.8x propodus. Moreover, E. guinean can be distinguished by the appearance of antennule: trapezoid article1, article2 0.6x article3, and the presence of bifurcated spine on uropod rami (Table II).
Maxilliped 1 (Figure 13(d)) basis stout, with a row of five plumose setae along inner margin, and with a bunch of setules on outer distal corner; endite with four plumose terminal setae (with thick basis), and with three plumose setae on medial surface; merus 0.4x carpus, with no setae; carpus 2x propodus, with seven flattened setae along lateral margin, with numerous setae on medial surface, and with seta on outer distal corner, and two short lateral setae on outer margin; propodus 2x dactylus, with 10 setae along inner and distal margin, and with two short setae and one long seta on outer margin laterally; dactylus with two simple terminal and three simple subterminal setae.
Maxilliped 3 (Figure 13(f)) basis 0.6x remaining articles combined, with crenulation along outer margin, distal prolongation reaching articulation of ischium and merus, with a row of eight plumose setae along inner margin, and with minute setae along outer margin; ischium 0.7x merus, with minute setae along inner margin; merus 1.4 L:W, 1.2x carpus, with plumose seta and a row of minute setae along inner margin, and with two plumose setae on outer distal corner; carpus 1.2 L:W, 1.4x propodus, with two simple setae on inner margin, and with short seta on outer distal corner; propodus 1.3 L: W, as long as dactylus, with two setae on inner margin; dactylus with three simple terminal setae, and with two simple subterminal setae.
Pereopod 1 (Figure 14(a)) basis 1.2x remaining articles combined, with three rows of minute setae along outer margin; ischium subequal to merus, with short simple seta on lateral margin; carpus 1.1x propodus, with no setae; propodus 0.9x dactylus, with short simple setae on lateral margin, and with two distal setae; dactylus with a row of 10 plumose setae along lateral and terminal margin. Exopod shorter than basis.
Pereopod 3 (Figure 14(c)) basis 0.9x remaining articles combined, with two simple setae on proximal half and with two simple setae at distal half; ischium 0.7x merus, with two simple setae on distolateral corner; merus 1.3x carpus, with simple lateral seta; carpus 1.3x propodus, with two simple lateral setae, and one simple and one bifurcated distally; propodus 3.2x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Pereopod 4 (Figure 14(d)) 0.9x remaining articles combined, with four simple setae and two plumose setae on medial surface and laterally, and with long simple seta on distolateral corner; ischium 0.5x merus, with two simple setae on distolateral margin; merus 0.9x carpus, with two long setae and short simple setae on lateral margins, and with two setae distally: one simple and one bifurcated; propodus 3.2x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Pereopod 5 (Figure 14(e)) basis 0.9x remaining articles combined, with no setae; ischium 0.7x merus, with two simple setae on distolateral corner, merus 1.2x carpus, with no setae; carpus 1.2x propodus, with simple seta laterally, and with three distal setae: one short and simple, one long and simple, and one long and bifurcated; propodus 3.2x dactylus, with strong bifurcated distal seta; dactylus terminated with one thin seta and one strong seta.
Antennule (Figure 16(a)) peduncle tri-articulated. Article 1 with parallel lateral margin, 2.2 L:W, 2.2x article 2, with a lateral row of nine simple and three plumose setae; article 2 0.6x article 3, with simple lateral seta and with two simple distal seta; article 3 3 L:W, with penicillate distal seta. Main flagellum two-articled, article 2 with two aesthetascs and with two simple setae. Accessory flagellum minute, tipped with penicillate seta.
Antenna not observed. Left mandible (Figure 16(b)) with a row of nine plumose setae, incisor with two teeth, lacinia mobilis with two teeth.
Right mandible (Figure 16(c)) with a row of nine plumose setae, incisor with two teeth.
Maxillula (Figure 16(e)) broad endite with 12 subterminal setae, and with a row of 20 plumose terminal setae. Outer endite with five plumose terminal setae, and two simple setae on outer subterminal margin. Inner endite with six plumose terminal 1074 A. Stępień et al. setae, and with simple short setae along inner margin. Maxilliped 1 (Figure 16(f)) basis stout; endite with five plumose strong terminal setae, and four plumose setae on medial surface, and with nine plumose setae along inner margin; merus 0.2x carpus, with no setae; carpus 2.6x propodus, with six flattened setae along inner margin, with numerous setae on medial surface, and with long plumose seta on outer distal corner; propodus 1.6x dactylus, with plumose seta on outer distal corner; dactylus with two simple terminal setae.
Maxilliped 2 (Figure 16(g)) basis 0.7x remaining articles combined, with two plumose setae on inner distal corner, and with simple seta on outer distal corner; ischium short, with no setae; merus 0.8x carpus, with simple distal seta; carpus 0.8x propodus, with five plumose setae along inner margin; propodus 2.3x dactylus with six plumose setae along inner margin, and with long plumose seta and minute seta on outer distal corner; dactylus with two strong simple terminal setae, and with four simple subterminal setae.
Maxilliped 3 (Figure 16(h)) basis stout, 0.7x remaining articles combined, with a row of short setae along lateral margins, and with plumose seta on inner distal corner, distal prolongation reaching articulation of ischium and merus, with six plumose setae along inner margin, and with two plumose setae on distal corner; ischium 0.5x merus, with three plumose setae along inner margin; merus 2 L:W, 2.8x carpus, with five plumose setae along inner margin, and with simple seta on outer distal corner; carpus 1.1 L:W, 0.5x propodus, with simple seta on outer distal corner; propodus 1.5 L:W, 1.4x dactylus, with two simple setae in distal half; dactylus with three simple terminal setae. Pereopod 1 (Figure 17(a)) basis 0.9x remaining articles combined, proximal part wider than distal, with no setae; ischium 0.4x merus, with short lateral seta; merus 0.8x carpus, with two simple lateral setae; carpus 1.2x propodus, with five simple lateral setae; propodus 1.4x dactylus, with two simple lateral setae, and with three distal setae; dactylus with three simple setae laterally, three terminal setae, and with simple subterminal seta. Exopod little longer than basis.
Pereopod 4 (Figure 17(d)) basis 1.3x remaining articles combined, with four simple setae on lateral margins; ischium 0.6x merus, with no setae; merus 0.9x carpus, with simple lateral seta; carpus as long as propodus, with simple lateral seta, and with two setae on distal corner; propodus 4x dactylus, with bifurcated seta and two simple setae on distal corner; dactylus short, terminated with one thin seta and one strong seta.
Pereopod 5 not observed. Uropod (Figure 17(e)) peduncle about 0.4x pleotelson, with short setae on lateral margin, and distal corner. Endopod one-articulated, with four simple setae on inner margin, and two spine on outer margin. Exopod two-articulated, subequal to endopod; second article with four simple setae along outer margin, terminated with two setulose setae. Distribution. The Gulf of Guinea, off the coast of Ghana, Eastern Atlantic; depth 20-50 m. Remarks. Eocuma nansenae, E. dollfusi, E. affine (only male known) and E. ferox share a similar distribution of the lateral horns and the shape of the carapace. However, the new species has a unique character in the form of the pseudorostrum tip which is located along the same line as the tip of the lateral horn. Other differences are: 1. The proportion of pereopod 1: in E. nansenae, dactylus is 0.6x propodus, while in E. dollfusi, dactylus is elongated (1.3x propodus), but it is short in E. affine and E. ferrox (0.8 and 0.7x propodus, respectively).
Antenna not observed. Left mandible (Figure 19(b)) with a row of nine plumose setae, incisor with three teeth, lacinia mobilis with four teeth.
Maxilliped 1 (Figure 19(f)) basis stout, with no setae; endite with five plumose terminal setae, and two hook setae and a row of six plumose setae along inner margin; merus 0.2x carpus, with two plumose setae on inner distal corner; carpus 1.3x propodus, with six flattened setae accompanied by one thin seta along inner margin, with numerous setae on medial surface, and with plumose seta on outer distal corner; propodus 2x dactylus, with eight plumose setae along inner margin, and with plumose setae on outer margin; dactylus with three long and one short simple terminal setae. Maxilliped 2 ( Figure 19(g)) basis 0.8x remaining articles combined, with two plumose setae on inner distal corner, and plumose seta on outer distal corner; merus 1.2x propodus, with plumose seta on distal surface, and numerous minute setae along outer margin; carpus 0.8x propodus, with five plumose setae along inner margin, propodus 2x dactylus, with seven plumose setae along inner margin, with plumose seta on outer distal corner, and with plumose seta on medial surface; dactylus with simple terminal seta, and five plumose subterminal setae.
Pereopod 3 (Figure 20(c)) basis as long as remaining articles combined, with four penicillate setae laterally, and simple seta laterally in distal part; ischium 0.5x merus, with simple seta laterally; merus 1.2x carpus, with simple seta laterally, and simple distal seta; carpus 1.3x propodus, with one distal seta, and one seta subdistally; propodus 3x dactylus, with bifurcated seta on distal corner; dactylus short, terminated with one thin and one strong seta.
Pereopod 5 (Figure 20(e)) basis 0.7x remaining articles combined, with two simple lateral setae in proximal part, and with simple lateral seta in distal part; ischium 0.7x merus, with no setae; merus as long as carpus, with simple lateral setae; carpus 1.4x propodus, with one seta on distal corner, and one subdistal seta; propodus 3.2x dactylus, with bifurcated seta on distal corner; dactylus short, terminated with one slender and one strong seta.
Uropod (Figure 20(f)) peduncle 0.4x pleotelson, with a row of four setae along lateral margin. Endopod one-articulated, with a row of eight setae along outer margin, terminated with setulose seta. Exopod two-articulated, article 2 with a row of seven setae and crenulation on outer margin, with three setae on inner margin, and with two fine terminal setae.
Distribution. The Gulf of Guinea, off the coast of Ghana, Eastern Atlantic; depth 50-250 m.
Remarks. The presence of lateral horns and their direction renders E. olokunae similar to E. lanatum and E. aculeatum. The new species shares crenulation on the uropod exopod with E. lanatum, the presence of tubercles on the carapace being shared with E. aculeatum.
Eocuma olokunae can be distinguished from E. lanatum by the position of the horns. In the new species, the tip of the horns does not reach the tip of the rostrum, as is the case in E. lanatum. Moreover, the proportion of antennule article 3 is different: 3 L:W in E. olokunae sp. nov. and 7 L:W in E. lanatum (Bochert and Zettler 2011), ( Figure  16). Another small difference observed concerns the proportion of carpus to propodus in pereopod 1 which is 0.7x propodus in the new species and 0.5x in E. lanaum. E. olokunae is distinguished from E. aculeatum by the absence of long minute setae that form a dense cover on the carapace of E. aculeatum. In addition, the proportion of pereopod 1 in both species is different: in the new species, carpus is shorter than propodus (0.7x), and propodus is 2.5x dactylus. In E. aculeatum, carpus is 1.3x propodus and 1.1x dactylus. Moreover, a strong spine on distal corner of pereopod 2 merus allows us to distinguish E. olokunae sp. nov. from E. aculaetum, with its unarmed pereopod 2 merus.

Diversity
So far, the genus Eocuma has been known to include seven species from the tropical coasts of Africa (Jones 1957;Bochert & Zettler 2011). Jones (1956) summarised the distribution of the shallowwater Cumacea and suggested tropical African coasts to support one of the poorest recognised fauna, compared to other tropical areas. However, Menegotto and Rangel (2018) refer to a severe lack of funding for science and an inadequate scientific infrastructure as the real causes of the inadequate knowledge of the African marine fauna. Thus, the current state of knowledge is more of an artefact that needs to be readdressed, especially since the area is Diversity of Atlantic Eocuma intensively exploited commercially for its oil and gas resources (Friedlander et al. 2014;Pabis et al. 2020).

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A. Stępień et al. Buhl-Mortensen et al. 2017;Sobczyk et al. 2021;Jóźwiak et al. 2022). The high diversity and the presence of rare species allow us to regard the marine fauna of West Africa as unique and poorly known. For this reason, waters off the Atlantic coast of West Africa should be granted an effective environmental protection. Moreover, considering the general underestimation of marine diversity (Appeltans et al. 2012), it is expected that many more new peracarid species will be discovered, provided the earlier-unexplored areas are properly sampled and protocols appropriate for the collection and processing of macrobenthos samples are adhered to (Brandt et al. 2016;Frutos et al. 2022;Stefanni et al. 2022).

Phylogenetic analysis
The analysis presented here is the first attempt to explore the relationship between the Eocuma species and their possible routes of dispersal; it might be treated as a background for future studies. Nevertheless, the analysis carries a burden of many uncertainties. The high level of character polymorphism in the Cumacea (Haye 2007) in general, and in the genus Eocuma in particular, hinders recognition of clear patterns in its relationships. A similar problem is encountered in many other crustacean taxa. The high plasticity, sexual polymorphism and ontogenetic variation present obstacles to resolving the systematic position if the analysis is based on morphological characters only (Larsen & Wilson 2002). A more advanced analysis, including molecular assays, is needed here (Frutos et al. 2022). All four trees developed here, and thus the consensus tree, revealed similar patterns, i.e. three sister groups within the genus Eocuma. The first group includes E. elongatum and E. victoriae, which originally were assigned to the genus Mossambicuma  Calman (1904Calman ( , 1907aCalman ( , 1907b; Zimmer (1914); Fage (1928Fage ( , 1950; Kurian (1951Kurian ( , 1954; Gamô (1967Gamô ( , 1976; Le Loeuff and Intès (1972); Day (1978); Kurian and Radha Devi (1983); Mühlenhardt-Siegel (1996); Petrescu (1998Petrescu ( , 2003; Patel et al. (2003); Corbera et al. (2005); Corbera and Galil (2007); Bochert and Zettler (2011); Kim et al. (2020); Watling and Gerken (2022). genera and later synonymised with Eocuma (Haye, 2007). Although the clade with these two species is separated, this separation is not supported by strong statistical evidence.
Other Eocuma species were grouped into one clade, with three species separated as ancestral. The most outlying species, E. fovellatum, lacks horns and its carpus and pereopod 3 propodus are of an almost equal length, as in Upselapsis which is regarded as the ancestral taxon. Eocuma dollfusi was separated because its pereopod 1 basis is shorter than the length of the ischium, merus, carpus, propodus and dactylus combined, and the dactylus is shorter than the propodus; the separation of E. nansenae is due to the pseudorostrum being situated at the level of the horns, and because of a narrow ocular lobe. Although these characters are highlighted as those separating E. fovellatum, E. dollfusi and E. nansenae sp. nov. from other Eocuma species, they can still be found in some Eocuma species, e.g. there is a lack of horns in E. ghanaian, or the pseudorostrum is at the level of horns in E. sarsii. All this confirms the relatively high level of polymorphism within Eocuma rather than proving that E. fovellatum, E. dollfusi and E. nansenae represent a distinct lineage.
The remaining Eocuma species were divided into two main lineages, the first containing species with a body of regular shape (oval in cross section) and the other including species with a flattened body, tapered posteriorly, with two pairs of horns. Although the division was present in all the four trees developed, the number of synapomorphic characters was too low to provide a strong statistic support. Moreover, some characters were not constant within the group, e.g. all of clade 56 species except E. ghanaian sp. nov. showing horns; all of clade 47 species showing horns; or most of clade 47 species having the carapace tapering towards the posterior, except for E. mandeli sp. nov. with the body oval in dorsal view.

Biogeography of Eocuma
Eocuma is a shallow-water taxon, occurring usually not deeper than 100 m (Day 1978;Corbera et al. 2005;Bochert & Zettler 2011), distributed in tropical and temperate zones. Seven new Eocuma species were collected on the Ghanaian shelf at depths of 23-100 m, but E. olokunae was also found deeper (250 m). So far, only E. aculeatum was found at a similar depth in the Mozambique Channel (Day 1978). The genus is clearly a warm-water taxon. The southernmost locations of Eocuma species are off South Africa (Day 1978); the northermost location was off the Kamchatka Peninsula in the Pacific (Marcusen 1894;Gamô 1967;Kim et al. 2020) and in the Atlantic's Bay of Biscay (Fischer 1872;Calman 1907).
Together with the seven previously described species ( Figure 21 and Table III), the TA region supports 14 Eocuma species, which makes it the second most diverse region for the genus, after the Indian Ocean (WIP). The latter, together with the Red Sea and the Persian Gulf, hosts 15 Eocuma species. In contrast, the Central Indo-Pacific (CIP) and the Tropical South Africa (TSA) support five and three species, respectively (Table III); four Eocuma species are known from both the north-west Pacific (TNP) and the Mediterranean Sea, two being known from the Bay of Biscay (TNA). Although relatively well studied, the Australian and New Zealand cumaceans (Petrescu 2004(Petrescu , 2006Gerken, 2013Gerken, , 2014Gerken, , 2016Gerken, , 2018 include as few as two Eocuma species. Results of our analysis show the fauna occurring off West Africa (TA) to be diverse, unique and clearly different from the faunas of other Atlantic and non-Atlantic locations. Only one species recorded off the African coast (E. ferrox) was found in the eastern and central Mediterranean Sea. Briggs and Bowen (2013) reported four potential sources of Eocuma species for the African fauna: (1) the Tethys Sea, (2) the Western Atlantic and Eastern Pacific before the Isthmus of Panama developed, (3) radiation in the Atlantic, and (4) the Indo-Pacific region via southern Africa. Given that Eocuma is a truly warm-water taxon, and that the fauna of south-east Africa and the Indian Ocean is clearly different from that of the western African coasts, the hypothesis of an Indian Ocean origin of the African fauna seems unlikely. Furthermore, the currents along the southern African coasts (i.e. the warm Agulhas Current and the cold Benguela Current) are not likely to facilitate migration of warm-water fauna from the Indian Ocean to the Atlantic. In the case of Eocuma species, the southeast African fauna is so different that the hypothesis of the Indian Ocean as the origin of the Atlantic fauna is impossible to defend. Although such a pattern of species dispersal has been reported for at least some animal groups (Floeter et al. 2008;Teske et al. 2014), the lack of fauna common to the Atlantic and non-Atlantic regions is evident and rules out such dispersal directions. It seems much more likely that the TA fauna is a descendant of the western Atlantic-eastern Pacific, the dispersal happening about 2.8 Ma ago (O'Dear et al. 2016). This hypothesis, however, seems untenable as well, as no species of the genus Eocuma has been found in the western Atlantic fauna, and the family Bodotriidae is poorly represented in this part of the world in general (Fischer 1872;Fage 1928Fage , 1950Le Loeuff & Intès 1972). In the fourth possible scenario (Briggs & Bowen, 2013), the tropical Atlantic fauna could have evolved in situ. Considering the multidirectionality of the dispersal (e.g. from and to the place of origin) and that fauna at the site of origin may have become extinct, and further assuming that the place of origin supports the highest diversity, erroneous conclusions may be drawn (Briggs, 2000(Briggs, , 2003Mironov 2006). At present, only one Eocuma species (E. ferox) has been reported from the western part of the Mediterranean Sea, and it is present along the western African coast. Although current distribution-based inferences regarding the place of origin are subject to some bias, it cannot be ruled out that the Mediterranean Sea, separated from the Tethys Sea by the Alpine orogeny prior to the Miocene, may have been the origin of the West African littoral fauna until the formation of the Strait of Gibraltar. Furthermore, the ancient Tethys Sea is regarded as a centre of radiation for the family Bodotriidae (Haye 2007). During the Triassic-Jurrasic mass extinction, the Tethys Sea became a centre of radiation for many taxa, including the Cumacea, which were later transported to the newly opening Atlantic and Indo-Pacific regions.

Disclosure statement
No potential conflict of interest was reported by the authors.