Alvinocaris costaricensis, Martin & Wall & Shank & Cha & Seid & Rouse, 2018

Martin, Joel W., Wall, Adam R., Shank, Tim, Cha, Harim, Seid, Charlotte A. & Rouse, Greg W., 2018, A new species of Alvinocaris (Crustacea: Decapoda: Caridea: Alvinocarididae) from Costa Rican methane seeps, Zootaxa 4504 (3), pp. 418-430 : 420-428

Alvinocaris costaricensis , new species

Material examined. Holotype: SIO-BIC C12202, female (TL ~ 42 mm, CL 17.4 mm, OCL 10.4 mm, carapace height 6.0 mm), Eastern Pacific Ocean , Costa Rica, Mound 12, Alvin dive 4503, 8.9307° N, 84.3072° W, 1005 m, collector Greg Rouse, Feb/24/2009 . Paratypes: SIO-BIC C13298, SIO-BIC C13299, same collecting data as for holotype; MZUCR-3569-01, same collecting data as for holotype. NHMLAC LACM CR 2009.1 (ex SIO-BIC C11140-1), ovigerous female ( OCL 17.6 mm, TL 55 mm), same collecting data as for holotype. SIO-BIC C11157 and C12203, Eastern Pacific Ocean , Costa Rica, Mound 12, Alvin dive 4511, 8.9305° N, 84.3123° W, 1001 m, collector Greg Rouse, March/5/2009; SIO-BIC C12203 1 badly damaged specimen (TL 13.2 mm, OCL 4.9 mm; abdomen disarticulated, sex undetermined). Although damaged, this specimen was sequenced and is the same species. SIO-BIC C11157 was sequenced and is the same species. SIO-BIC C11209, sex not determined, (TL 77.6 mm, CL 30.4 mm, OCL 17.1 mm; left side of carapace slightly inflated), Eastern Pacific Ocean, Costa Rica, Jaco Scarp, Alvin dive 4590, 9.1176° N, 84.8395° W, 1800 m, collector Greg Rouse, Jan/11/2010. SIO-BIC C11183, C11186, sex not determined, Eastern Pacific Ocean, Costa Rica, Mound 12, Alvin dives 4587 and 4588, 8.9307° N, 84.3072° W, 1005 m collector Greg Rouse, Jan/08 and 09/2010. These specimens were sequenced and are the same species .

Description. Body relatively robust for the genus, integument thin, smooth, shiny. Carapace ( Figs. 1 , 2 ) with strong suborbital spine ( Fig. 3A ) and well developed pterygostomial spine exceeding length of orbital spine, otherwise unarmed.

Rostrum ( Figs. 1B , 2 , 3A ) well developed (tip broken in holotype but well developed in several paratypes), extending forward and only slightly downward, with strong, sharp, anterior-curving teeth in row on dorsal border, extending backward to about, or slightly posterior to, midlength of carapace, bearing 5–7 weakly developed teeth along ventral border. Weak dorsal carina extending backward from rostrum along carapace to posterior border. Larger specimens with rostrum strongly up-turned distally, bearing up to 10 dorsal and forward-directed teeth, exceeding anteriorly beyond tip of scaphocerite and antennular peduncle.

Eighth thoracic sternite with well-developed and acute median tooth directed anteroventrally, produced beyond coxa of pereopod 5 and visible in lateral view ( Fig. 2 ).

Abdomen ( Figs. 1A , 2 ) well developed, somite 6 with sharp posteriorly directed tooth on either side extending posteriorly along telson ( Fig. 3D ); somite 5 with similar but shorter tooth and with acute posteroventral border; somite 4 with acute posteroventral border.

Telson ( Fig 2 , 3D, E ) long, exceeding length of uropods, lateral margins straight, slightly converging posteriorly; each lateral margin bearing row of 7 movable spines; posterolateral corners each with single large slightly medially-curved spine; posterior border bearing two pairs of small spines and 4 plumose setae; posterior border slightly indented as shown. Uropodal rami each with border of plumose setae; exopod broader than endopod, bearing diaresis and single lateral spine just posterior to acute tooth at border of diaresis, as shown ( Fig. 3D ).

Eyes fused mesially but distinct, each with small anterodorsal tubercle ( Fig. 3A ). Cornea with diffuse pigmentation internally but no clear pigmented layer or region.

Antennular peduncle ( Fig. 3C ) extending beyond antennal scale, with relative lengths of articles 1> 2> 3; article 1 with large lateral spine extending clearly beyond similar spine of article 2. Antennal scale ( Fig. 3B ) broad, distally rounded, with acute anterolateral tooth extending almost to full length of scale.

Mouthparts ( Fig. 4 A–F) typical of genus ( Komai & Segonzac 2005; Vereschaka et al. 2015).

First pereopod (cheliped) ( Figs. 1A , 2 , 3 F–H) well developed, long, extending beyond bases of antennae when outstretched; chela delicate for genus and strongly curved inward, bearing delicate pectinations along cutting borders of both fingers; fingers of chela approximately 1.5 times length of propodal palm; carpus cup-shaped to receive proximal end of propodus, and bearing brush of “cleaning setae” and large, acute tooth on inner margin.

Second pereopod ( Figs. 2 , 3 I–K) shorter than first; chela delicate, approximately 4 times longer than wide, both fingers bearing pectinate setal borders on cutting margin; fingers slightly exceeding length of palm; ischium with single movable ventral spine.

Third through fifth pereopods ( Fig. 5 ) similar, long and delicate; propodus longer than merus; merus longer than carpus. Dactylus short, stout, with recurved sclerotized tip and ventral single row of 4 or 5 short, sclerotized spines. Propodus with row of regularly spaced short spines along ventral border. Merus with 2 large, ventral movable spines on P3, none on P4 and P5. Ischium with 2 ventral movable spines on P3 and P4, none on P5.

Female pleopod ( Fig. 4G ) with subequal rami bearing plumose setae; appendix interna short, simple, tapering distally.

Coloration. Photographs of the holotype ( Fig. 1A ) and one paratype ( Fig. 1B ) show a largely translucent to white shrimp with a pale or beige carapace, some orange or reddish coloration on the mouthparts, and delicate red reticulations on the carapace and abdomen. The eye, although reflecting light in the photographs, appears to be orange-red.

Etymology. The specific epithet reflects the location of the methane seeps off the Pacific coast of Costa Rica.

DNA sequence analysis. The seven COI sequences for A. costaricensis n. sp. were very similar, with six (including that of the holotype) being identical, and one haplotype differing by only one base ( Fig. 6C ). These had a closest pairwise distance (of ~12%) to Alvinocaris komaii (GenBank KP759373 ) from West Pacific hydrothermal vents. Of the 505 bases in the COI dataset, 323 were constant, 158 were parsimony-informative, and 24 were variable but parsimony-uninformative. The ML analysis ( Fig. 6A ) recovered Alvinocaris as paraphyletic, with A. costaricensis n. sp. as the sister group to A. komaii . The Rimicaris + Opaepele + Shinkaicaris clade was nested within Alvinocaris as sister to the A. costaricensis n. sp. + A. komaii clade, though this, and most other deeper nodes, had low support. The four-known seep-dwelling alvinocaridids, A. methanophila , A. muricola , A. stactophila and A. costaricensis n. sp., were scattered across the phylogeny and all had hydrothermal vent-dwelling taxa as sister groups. The MP analysis ( Fig. 6B ) found eight shortest trees of length 547. These eight trees varied only slightly; one of the most parsimonious trees with the same topology as the majority-rule consensus tree, and that of the of majority-rule consensus tree for the parsimony jackknife analysis, is shown in Fig. 6B . The MP analysis recovered a monophyletic Alvinocaris (with the exception of A. methanophila ), though with poor support; as in the ML results, A. costaricensis n. sp. was sister group to A. komaii .

Remarks. Morphological comparison. Alvinocaris costaricensis n. sp. is a large species for an alvinocaridid, with some paratypes (e.g. SIO-BIC C11209 from the Jaco Scarp site) exceeding 75 mm TL and 64 mm OCL. The species is easily identifiable as a member of Alvinocaris based on several characters uniquely shared by members of that genus: the laterally compressed, well-developed and toothed rostrum, dentate posterior border on abdominal somite 4, minute dorsal tubercle on the surface of the eye, strongly curved and minutely pectinate chelae, small ischial spine on the second pereopod, parallel rows of small spines on the telson, and spination of pereopods 3 and 4, among other characters ( Komai & Segonzac 2005, Vereschaka et al. 2015).

Among species of Alvinocaris , the new species is similar to A. muricola and also to A. kexueae in the size (length) of the rostrum, the orientation of the dorsal rostral spination, and the relatively shallow dorsal angle of the carapace. In all three species, the rostrum slopes more gradually, and bears larger teeth, than in most Alvinocaris species ( Komai & Segonzac 2005). However, there is much morphological variation in the rostrum of A. muricola . Using the diagnostic key to species provided by Komai & Segonzac (2005), the new species keys to Alvinocaris lusca , another eastern Pacific (Galapagos Rift and East Pacific Rise) species, based on the number of ventral rostral teeth (fewer than 5) and the length/width ratio of the antennal scale. Additionally, A. lusca is one of the few species of Alvinocaris that shares with the new species, a slightly indented posterior border of the telson (though not as indented as in A. costaricensis ). However, A. costaricensis differs from A. lusca in having a far slenderer major cheliped, 2 (rather than 3) ventral meral spines on pereopod 3, and a much longer lateral spine on the basal article of the antennal peduncle, which barely exceeds the length of the spine of the second article in A. lusca .

An interesting departure from typical species of Alvinocaris is the absence of ventral meral spines on pereopod 4. Komai and Segonzac (2005) considered the presence of these spines on pereopods 3 and 4 diagnostic for the genus Alvinocaris . The new species has prominent meral spines on P3, but not on P4 or P5 indicating that the generic diagnosis requires slight amendment. This difference does not warrant the erection of another genus, as all other characters fit well within the known range of features described for the other 16 species of Alvinocaris . The indented terminal border of the telson is also unique among species in the genus, with A. lusca being the closest match in that character. However, variation in this character is known ( Komai & Segonzac 2005), so we hesitate to suggest this as a determining feature for field identification.

Molecular comparison. We place the new species in Alvinocaris , even though there is evidence from the ML analysis (albeit weakly supported) ( Fig. 6A ) that the genus, as currently construed, could be paraphyletic (and polyphyletic when A. methanophila is considered). However, further sequence data are required to properly resolve this situation, and that question is beyond the scope of this study. Vereshchaka et al. (2015) also found a paraphyletic Alvinocaris based on their analysis of COI and also of the available 16S rDNA sequences, but maintained the genus as currently formulated, although they suggested that the sequence for A. methanophila on GenBank ( AY163260 ) was the result of incorrect identification or processing of the material. Vereshchaka et al. (2015) did recover Alvinocaris (including A. methanophila ) as a well-supported clade based on morphology, and A. costaricensis n. sp. shared these features (notably the laterally compressed and carinate rostrum, eyes fused medially with each bearing a small tubercle, and paired dorsal spines on the telson).

Co-occurring species. Another, and smaller, alvinocaridid species, differing both morphologically (with a shorter rostrum lacking the extensive dorsal teeth seen in A. costaricensis ) and molecularly, was also collected from the Mound 12 site (AD 4501, 1008 m depth). Further specimens of that species in the SIO collection represent yet another undescribed species.

*Formerly in Chorocaris, synonymized with Rimicaris by Vereshchaka et al. (2015).

Figures

FIGURE 1. A, Alvinocaris costaricensis new species, holotype female, SIO-BIC C12202, Eastern Pacific Ocean, Costa Rica, live color photograph. B, same species, paratype female, C11186.

FIGURE 2. Alvinocaris costaricensis new species, holotype female, SIO-BIC C12202, Eastern Pacific Ocean, Costa Rica, lateral view, extremity of rostrum broken. Carapace length 10.4 mm (measured from back of the orbital sinus in a straight line to posterior border of carapace).

FIGURE 3. Alvinocaris costaricensis new species, holotype female, SIO-BIC C12202, Eastern Pacific Ocean, Costa Rica. A, eye and section of rostrum (above) and orbital spine (below); note minute dorsal tubercle on eye. B, antennal scale, right side, dorsal view. C, antennular peduncle, right side, dorsal view. D, telson and left uropods, dorsal view. E, extremity (approximately distal half) of telson. F, pereopod 1 (cheliped), right side, ventro-lateral view. G, pereopod 1, dorsal view. H, higher magnification of pereopod 1, dorsal inner view. I, second pereopod, right side, lateral view. J, pereopod 2 propodus and chela, outer view. K, pereopod 2 chela, inner view.

FIGURE 4. Alvinocaris costaricensis new species, holotype female, SIO-BIC C12202, Eastern Pacific Ocean, Costa Rica. A, left mandible, inner view. B, maxilla, inner view. C, maxilliped 1. D, maxilliped 2. E, maxilliped 3, lateral view. F, maxilliped 3 dactylus, inner view. G, first pleopod and appendix interna, right side.

FIGURE 5. Alvinocaris costaricensis new species, holotype female, SIO-BIC C12202, Eastern Pacific Ocean, Costa Rica. A, pereopod 3, left side, lateral view. B, same, close up of dactylus and distal half of propodus. C, pereopod 4, left side, lateral view. D, close up of dactylus and distal half of propodus. E, pereopod 5, left side, lateral view. E, close up of dactylus and distal half of propodus.

FIGURE 6. Relationships among selected members of Alvinocarididae based on COI sequence data. A, Maximum likelihood topology; numbers at nodes indicate bootstrap values. B, one of eight shortest trees from the maximum parsimony analysis of COI matching jackknife consensus tree; numbers at nodes refer to parsimony jackknife score. C. Haplotype network generated by TCS (Clement et al. 2002); holotype and 5 paratypes have identical COI sequences; paratype C11186 differs by one base. Generic type species indicated (Type). Seep-dwelling species indicated (S).