Paralomis alcockiana, Hall, Sally & Thatje, Sven, 2009

Hall, Sally & Thatje, Sven, 2009, Four new species of the family Lithodidae (Decapoda: Anomura) from the collections of the National Museum of Natural History, Smithsonian Institution, Zootaxa 2302, pp. 31-47 : 32-35

Paralomis alcockiana n. sp.

( Figs 1 , 2 )

Material examined. South Carolina: 31°20’N, 79°05’W, 1995, 570 m: male holotype, CL 44 mm ( USNM 269032), S. Carolina Department of Natural Resources.

Etymology. This new species is named after Alfred W. Alcock, 19th century British carcinologist, and Fellow of the Royal Society who reported on the findings of the HMS Investigator in the Indian Ocean.

Description of holotype. Carapace about as long as broad; irregularly hexagonal and angular in outline ( Fig. 1 a). Surface covered in smoothly elliptical, raised tubercles becoming somewhat more acute towards anterolateral margins; some tubercles enlarged and more acute, with clustered rings of smaller tubercles at base ( Fig. 1 b). Gastric regions with five enlarged tubercles, largest in the centre of region. Cardiac region with four enlarged tubercles in a quadrilateral pattern. Branchial region with three enlarged tubercles. (Positions of enlarged tubercles corresponding to dorsal spines in other species of Paralomis such as P. f o r m o s a Henderson). Under magnification, all tubercles with irregular arrangements of very short setae, as seen in Paralomis cubensis ( Fig. 1 d).

No regions particularly inflated above dorsal surface, although gastric region slightly inflated in comparison to branchial and cardiac regions. Grooves delimit cardiac region, forming triangle in advance of posterior margin. Small anterior spine present on pterygostomian region, as typical of genus.

Median rostral spine nearly straight, surpassing length of ocular peduncle; ventral surface deeply keeled, bearing several small denticulate spinules ( Fig 2 a). Paired dorsal spines diverging at level of cornea; both spines much shorter than ventral spine ( Figs 2 a, b). Dorsally, base of rostrum covered with more or less acute tubercles. Base of the rostrum wide, partially obscuring bases of ocular peduncles in dorsal view.

External-orbital and anterolateral spine similar in size, shorter than ocular peduncle ( Fig. 1 a). Several irregularly spaced spines (10+) of varying size on lateral margins of anterior half of carapace. Posterior lateral margins with acute tubercles.

Ocular peduncles covered with short spines, and one larger spine disto-dorsal near cornea ( Fig. 1 c). Antennal acicle broad, with one large central spine, 4 or 5 long spines on outer border and 4 spines of similar length on inner border.

Cheliped merus with numerous spiniform tubercles dorsally and on outer surface, larger distally, and one large spine distally on inner surface. Chela with numerous tufts of long yellow setae covering palm and fingers of both hands.

Merus of pereiopod 3 a little over half carapace length, and about four times as long as high, rectangular in cross-section. Several rows of spines on dorsal anterior margin and ventral posterior margin. Posterior, dorsal and ventral surfaces of merus covered with acute tubercles. Two rows of spines on dorsal surface of carpus, larger on anterior row. Propodus with one row of dorsal spines and one row of ventral spines; covered in acute tubercles. Dactylus ventral margin with row of long black needle-like spines, and one black spine at tip; dorsal margins with a few spines near the articulation with propodus; with tufts of long yellow setae.

Abdomen covered with tubercles smaller than on dorsal surface. Marginal plates expanded and fused on each of abdominal segments 3–5; marginal plates fused to lateral plates on segment 3 ( Fig. 2 d).

Remarks. Paralomis alcockiana n.sp. shares many characteristics with P. cubensis , which is found in the Gulf of Mexico and Caribbean Sea ( Chace 1939) at similar depths to the new species. Some differences are listed in Table 1 . The most notable distinguishing feature is the presence, in P. alcockiana , of some enlarged conical tubercles surrounded by a ring of smaller rounded tubercles ( Fig. 1 b).

P. alcockiana n. sp. ( Figs 1 , 2 ). P. cubensis Chace, 1939 P. arethusa Macpherson, 1994

Carapace outline Irregularly hexagonal. Circular in juveniles. Pyriform in Hexagonal.

adults.

Paralomis alcockiana is similar in shape to P. arethusa from the Barbados accretionary prism, a species known only from a juvenile specimen of 18 mm CL. Although comparison is difficult between different growth stages ( Ingle & Garrod 1987), some key diagnostic differences are listed in Table 1 .

Paralomis alcockiana is somewhat similar to P. i n c a Haig, 1974, from Peru, and P. grossmani Macpherson, 1988 b, from French Guiana, but under magnification, the setal coverage of the dorsal tubercles is very different. Paralomis alcockiana has rounded tubercles sparsely covered with a few short setae; P. i n c a has rounded or conical tubercles, densely covered with short setae on their apices; and P. grossmani has a distinct ring of longer setae around the apex of the tubercles on its dorsal surface. There are also differences in the shape of the carapace. P. grossmani is longer and thinner than P. alcockiana , especially in the anterior region, and has the gastric region inflated to a much greater level. P. i n c a has its posterior half very much expanded, in contrast to P. alcockiana which has a roughly hexagonal outline.

Figures

FIGURE 1. Paralomis alcockiana n. sp. a – c: male holotype, 44 mm CL (USNM 269032), South Carolina: 31 ° 20 ’ N, 79 ° 05 ’ W, 570 m. (a) carapace, dorsal. (b) carapace ornamentation, dorsal. (c) part of ocular peduncle visible below rostrum, dorsal. Paralomis cubensis Chace. d, e: Male, 46 mm CL (USNM 213542) (d) carapace, dorsal. (e) carapace ornamentation, dorsal. Scale bar = 5 mm for a, d; 1 mm for b, c, e.

FIGURE 2. Paralomis alcockiana n. sp. a – f: male holotype, 44 mm CL (USNM 269032), South Carolina: 31 ° 20 ’ N, 79 ° 05 ’ W, 570 m. (a) anterior carapace, lateral. (b) rostral spines, dorsal. (c) right antennal acicle, dorsal. (d) abdomen. (e) right chela, lateral. (f) whole organism, dorsal. Scale bar = 1 mm for a – c; 5 mm for d – f.

Tables

TABLE 1. Key diagnostic differences between Paralomis alcockiana and two similar species.

Spinulation of lateral margins of carapace	Several irregularly spaced spines (10 +) of varying size on lateral margins of anterior carapace. Posterior lateral margins with acute tubercles.	More than 20 spines of different sizes spaced evenly around anterior and posterior margins	Three spines on each side of anterior margins, several small tubercles on posterior margins.
Spinulation of eyestalks	Several small spines or conical tubercles, largest terminal, extending well beyond cornea.	Several small spines or conical tubercles, largest terminal, extending well beyond cornea.	One distodorsal spine.
Antennal acicle	Broad; one large central spine, 4 or 5 long spines on outer border and 4 spines of a similar length on inner border.	4–6 spines, terminal pair longest, forming a fork. One spine proximal of inner spine of terminal pair and a fourth still more proximal on outer margin.	Large central spine not overreaching antennal peduncle; 2 spines on outer border. Inner border smooth.
Walking leg spinulation	Covered with irregular rows of spines and acute tubercles.	Covered with irregular rows of spines and acute tubercles.	Comb-like sets of spines on merus and carpus. Similar to P. serrata and P. pectinata from the Gulf of Mexico. Distinguishes all three in this group from P. alcockiana .