Cerapus slayeri, Drumm, 2018

Drumm, David T., 2018, Two new species of Cerapus (Crustacea: Amphipoda: Ischyroceridae) from the Northwest Atlantic and Gulf of Mexico, Zootaxa 4441 (3), pp. 495-510 : 496-503

Cerapus slayeri n. sp.

( Figs 1–6 )

? Cerapus sp. B sensu LeCroy, 2007: 556, fig. 481.

Material examined. Type material.— Holotype: male (♂), 4.0 mm, ( USNM 1488279 ), Delaware Bay, 38°58ʹ56.50ʺN 75°02ʹ43.8ʺW, salinity: 29.42 ppt . Allotype: female (♀), 3.8 mm, ( USNM 1488280 ), same locality as holotype .

Paratypes: 5 females (max. 3.8 mm), 5 males (max. 5.0 mm), (USNM 1488281); all same locality as holotype. 1 male (3.0 mm), 2 females (3.5 mm), 13 subadults, 3 juveniles ( USNM 1488282 ), Great South Bay , New York, 40°40ʹ52.14ʺN 73°14ʹ16.7994ʺW, salinity: 30.55 ppt.

Additional material: 80 females, 35 males, 183 juveniles retained in the author’s (DTD) collection at EcoAnalysts, Inc.

Diagnosis. Rostrum short and apically acute. Male antenna 1, peduncle 3 × as long as flagellum, peduncular article 1 slightly shorter than articles 2 and 3 which are slender and subequal in length. Male antenna 1 flagellum, 3 or 4 (rare)-articulate; female flagellum 3-articulate. Male and female antenna 2 with 3-articulate flagellum. Male and female antenna 1 and antenna 2 peduncle with pigment bands. Male pereonite 1 without a lateral keel. Male gnathopod 2 “palmer” margin of carpus with process near propodus articulation. Pereopod 7, posterior margin of basis with spinules extending more than three quarters distally and the carpus with posterodistal groups of long setae as well as anterodistally. Pleopod 2, inner ramus reduced, approximately 3 × as long as wide. Male uropod 1 peduncle with a large distoventral hook.

Description of male. Size, 4.0 mm ( Figs 1 , 2A ). Rostrum short, apically acute, length 0.1 × head; lateral cephalic lobe with ventral corner rounded. Sternal keel absent on pereonites 1 and 2.

Antenna 1 ( Figs 2A, B ) about half body length; peduncle 3 × as long as flagellum, peduncular article 1 slightly shorter than articles 2 and 3 which are slender and subequal in length; dorsal margin moderately convex; peduncular articles 2 and 3 with pigment bands; flagellum 3-articulate, article 1 with several aesthetascs and approximately 1.4 × as long as articles 2 and 3 combined, articles 2 and 3 with one aesthetasc. Antenna 2 ( Fig. 2A ) slightly longer than antenna; peduncle approximately 2.5 × as long as flagellum, articles 4 and 5 with pigment bands; flagellum 3-articulate, article 1 approximately 1.5 × as long as articles 2 and 3 combined.

Mandibles ( Figs 2C, D ): left and right incisors with six teeth; left lacinia mobilis with five teeth, right with one large tooth and minutely denticulate margin; left mandible with three broad accessory spines and one intermediate plumose seta; molar seta present on left mandible; palp article 2, 1.25 × as long as article 3, with two small simple setae; article 3 with 11 setae. Maxilla 1 ( Fig. 2E ): inner plate small with one apical plumose seta reaching tip of outer plate; outer plate with ten spine-teeth; palp biarticulate with six subterminal setae and five terminal spines. Maxilla 2 ( Fig. 2F ): outer plate broader than inner plate, both plates apically setose; inner plate with setae along medial margin. Maxilliped ( Fig. 2G ): inner plate subquadrate with four stout nodular spines and ten plumose setae; outer plate with three stout apical setae and eight stout nodular spines along medial margin, thirteen submarginal setae present; palp articles 2 and 3 with several long simple setae; article 4 with one long and one short terminal pectinate spiniform seta.

Gnathopod 1 ( Fig. 2H ) subchelate; coxa small; carpus subequal in length to propodus; 1.25 × as long as deep with setose posterior lobe; propodus 1.4 × as long as deep with four rows of anteromedial setae, palm extremely oblique, setose; dactylus with posterior row of short spinules. Gnathopod 2 ( Fig. 3A ) carpochelate; coxa larger than coxa 1, broader than deep; basis with short, sparse setae along anterior margin and fewer setae on posterior margin; carpus massive, 1.2 × as long as deep, palmer margin oblique with long posterior defining tooth and shorter tooth adjacent to propodus articulation; propodus approximately 2.4 × as long as broad, not recurved, with short setae on anterior and posterior margins; dactylus 0.8 × as long as propodus with short setae along posterior margin.

Pereopod 3 ( Fig. 3B ): coxa anteriorly produced, more than twice as broad as deep; basis 2.2 × as long as broad, with short setae on anterior margin and four longer setae (two setulate and two simple) on anteroproximal corner; ischium 1.75 × as long as wide; merus as long as broad; carpus with six setulate setae along distal half of posterior margin; propodus with six setulate setae on posterior margin. Pereopod 4 ( Fig. 3C ) nearly identical to pereopod 3, with fewer setae on anterior margin of basis. Pereopod 5 ( Fig. 3D ): coxa 1.6 × as broad as deep; basis about as long as broad; merus, posterior lobe with four plumose setae, smaller anterior lobe with one small seta; carpus, posterior lobe covered in denticles and bearing a seta; dactylus with one small accessory hook. Pereopod 6 ( Fig. 3E ): coxa 1.67 × as broad as deep; basis 1.8 × as long as broad, with short setae on anterior and posterior margins; ischium about as long as broad; merus 1.8 × as long as broad, with long and short setulate setae on posterodistal corner and simple setae on anterior margin and anterodistal corner; carpus slightly longer than broad with several long setulate setae on posterodistal corner and simple setae on anterodistal corner; propodus shorter than merus with several long and short simple setae on anterodistal corner and a few short posterodistal setae; dactylus with two small accessory hooks. Pereopod 7 ( Fig. 3F ): coxa 1.6 × as long as deep; basis with spinules on most of posterior margin and several short simple setae; ischium with two short anterodistal setae; merus with posterodistal and anterodistal groups of long setulate and simple setae; carpus shorter than merus with posterodistal and anterodistal groups of long setulate and simple setae; propodus slightly longer than carpus with posterodistal and anterodistal groups of long setulate setae; dactylus with two small accessory hooks and one subdistal short simple seta.

Pleopods 1 to 3 decreasing in size. Pleopod 1 ( Fig. 4A ): peduncle with two small distomedial hooks and two distal plumose setae; rami subequal in length, outer ramus broader than inner. Pleopod 2 ( Fig. 4B ): peduncle with two small distomedial hooks and three plumose setae; inner ramus reduced, about 3 × as long as broad, with six setae and appearing to be biarticulate; outer ramus almost twice as long as inner ramus, appearing to be triarticulate. Pleopod 3 ( Fig. 4C ): peduncle with two small distomedial hooks and lacking setae; inner ramus reduced, about twice as long as broad, 1-articulate with two setae; outer ramus twice as long as inner ramus, 1- articulate.

Uropods ( Fig. 4D ): Uropod 1 biramous; peduncle 3 × as long as wide, with two simple outer distal setae and one large distoventral hook; outer ramus with outer row of spinules and six medial setae and one large apical spine; inner ramus 0.6 × as long as outer ramus, with large apical spine. Uropod 2 uniramous; peduncle 3.4 × as long as broad, 5 × as long as vestigial ramus; ramus with two hooks and one subdistal seta. Uropod 3 uniramous; peduncle 2.1 × as long as broad, with one seta on inner margin; ramus vestigial with two hooks and one short robust seta. Telson broader than long, cleft halfway, each lobe with about 28 recurved hooks in four rows and pair of penicillate setae on inner distal corner.

Description of female. Similar to male except for the following: smaller size at maturity (max 3.8 mm). Pereonite 1 shorter and pereonites 4 and 5 longer than in male ( Fig. 5A ). Gnathopod 1 (not illustrated) basis anterior margin with proximal spinules; carpus with long setae midway on anterior margin. Gnathopod 2 ( Fig. 5B ) subchelate, larger but similar to gnathopod 1. Pereopod 5 coxa ( Fig. 5A ) larger. Uropod 1 peduncle ( Fig. 5C ) without distoventral hook. Telson ( Fig. 5C ) with two terminal rows of recurved hooks (but see section on intraspecific variation below). Oostegites on gnathopod 2 to pereopod 5.

Description of subadult male (2.5 mm). Similar to adult male except for the following: gnathopod 2 ( Fig. 6C ) carpus without “palmar” process. Appendages less setose.

Intraspecific variation. One male antennule had 4 flagellar articles on the left antennule and 3 flagellar articles on the right antennule. The mandibular palp can have varying numbers of setae. For instance, one male had three setae on article 2 and ten setae on article 3 ( Fig. 6A ). Another male had four setae on article 2 and thirteen setae on article 3 (not illustrated). One male telson had two rows of about 16 recurved hooks on each lobe ( Fig. 6B ). Larger individuals in general tend to be more setose than smaller individuals.

Etymology. Named after the thrash metal band, Slayer, who has a song entitled “Beauty Through Order,” which reminds the author of an homage to taxonomy.

Remarks. Cerapus slayeri n. sp. keys out to C. thomasi Ortiz and Lemaitre, 1997 using the key in Zeina and Asakura (2017) but can be distinguished by having 3 articles in the antenna 1 and antenna 2 flagella, mandibular palp article 2 with setae, and the pereopod 7 basis having spinules on most of the posterior margin. It is also a larger species. The only other described species with males having a distoventral hook on the first uropod peduncle is C. cudjoe Lowry and Thomas, 1991 , occurring in Southeast Florida and the Gulf of Mexico, but C. slayeri can be distinguished by the males lacking a lateral keel on pereonite 1, antenna 1 flagellum of male usually with 3 articles, shape of the male cheliped propodus (2.4 × as long as broad compared to 3.5 × in C. cudjoe ), and pereopod 7 basis anterior margin lacking long setae. It is possible that this species is the partially described Cerapus sp. B sensu LeCroy (2007), occurring from South Carolina to eastern Florida. The only major difference appears to be the pigment bands in the antenna 1 and 2 (lacking in Cerapus sp. B). The only described species of Cerapus in the Northwest Atlantic north of Florida is C. tubularis , but can be distinguished from C. slayeri by males lacking a distoventral hook on the uropod 1 peduncle, male antenna 1 flagellum with 2 articles, “palmar” margin of male gnathopod 2 with a median process, and pereopod 7 basis lacking spinules on posterior margin.

Cerapus is a taxonomically difficult genus of amphipods because of a lack of detailed studies of variation ( LeCroy 2007). It is shown in the present paper that the number of rows of hooks on the telson, number of antenna 1 flagella articles, and number of setae on mandibular palp and other appendages, can be quite variable.

Geographic distribution. Known only from Delaware Bay (type locality) and Great South Bay, New York ( Fig. 7 ).

Figures

FIGURE 1. Cerapus slayeri n. sp., male (top) and a specimen in its tube with protruding antennae (bottom).

FIGURE 2. Cerapus slayeri n. sp., adult male. A, holotype male, habitus (lateral view); B, head and antenna 1 peduncle (dorsal view); C, left mandible; D, right mandible (palp not illustrated); E, maxilla 1; F, maxilla 2; G, maxilliped; H, gnathopod 1. Scale bars: A = 0.5 mm; B = 0.2 mm; C-G = 0.05 mm; H = 0.1 mm.

FIGURE 3. Cerapus slayeri n. sp., adult male. A, gnathopod 2; B, pereopod 3; C, pereopod 4; D, pereopod 5; E, pereopod 6; F, pereopod 7. Scale bars = 0.1 mm.

FIGURE 4. Cerapus slayeri n. sp., adult male. A, pleopod 1 (setules on plumose setae are only shown for the distal setae); B, pleopod 2; C, pleopod 3; D, urosome and uropods; E, uropod 1 (ventral view). Scale bars: A, D = 0.1 mm; B, C = 0.05 mm.

FIGURE 5. Cerapus slayeri n. sp., adult female. A, allotype female, habitus (lateral view); B, gnathopod 2; C, urosome and uropods. Scale bars: A = 0.5 mm; B,C = 0.1 mm.

FIGURE 6. Cerapus slayeri n. sp. A, adult male, mandibular palp; B, adult male, urosome and uropods; C, subadult male, gnathopod 2. Scale bars: A = 0.05 mm; B,C = 0.1 mm.

FIGURE 7. Map showing collection sites for Cerapus slayeri n. sp. in the Northwest Atlantic. The black square in Delaware Bay represents the type locality.