A New Species of Crangonid Shrimp of the Genus Philocheras (Crustacea: Decapoda: Caridea) from Hawai'i

Abstract

Philocheras breviflagella, a new species of crangonid shrimp, is described and illustrated on the basis of a single ovigerous female collected from O'ahu, Hawai'i, at subtidal depth. The new species is most similar to P. sabsechota (Kemp, 1911) known with certainty only from the Andaman Islands, eastern Indian Ocean. It differs from P. sabsechota in several features, including the much narrower rostrum, the unarmed second lateral carina of the carapace, and the truncate posterior margin of the uropodal exopod. Other differences include the shorter fingers (each with an elongate unguis) of the second pereopod, and medially notched posterodorsal margins of the second and fourth abdominal somites. The new species is the first representative of the genus found to occur in the central Pacific.

The genus Philocheras Stebbing, 1900, is the most speciose among the Crangonidae, including nearly 50 species worldwide (de Man 1920, Holthuis 1951, 1961, Yaldwyn 1960, 1971, Zarenkov 1968, Crosnier 1971, Fujino and Miyake 1971, Dardeau 1980, Chace 1984, Wicksten 1989, Burukovsky 1990a,b, Bruce 1994, De Grave 2000, Kim and Hayashi 2000). Although Kemp (1911) synonymized Philocheras with Pontophilus Leach, 1817, the genus was revived on the basis of the laterally unarmed rostrum, the absence of a postorbital suture on the carapace, and the absence of an exopod on the first pereopod (Chace 1984). Christoffersen (1988) showed that Philocheras is a clade, characterized by one autapomorphy (the antennular stylocerite is transversely oblong) and one homoplasy (the exopod is absent from the first pereopod). Philocheras is well represented in the Indo-West Pacific by 19 species, but there has been no record of the genus from the central Pacific, including Hawai'i.

During an ongoing study of Crangonidae in the Indo-Pacific, a small ovigerous specimen from O'ahu, Hawai'i, was made available for study by Dr. P. K. L. Ng of the National University of Singapore. Detailed examination has shown that this specimen represents a distinct undescribed species of Philocheras. Although only a single specimen was available for examination, its distinctiveness has led me to describe it as a new species, P. breviflagella. This new species represents the first record of Philocheras in the central Pacific.

The holotype is deposited in the Raffles Museum of Biodiversity Research, National University of Singapore (ZRC). The abbreviation "cl" indicates postorbital carapace length. The drawings were made with the aid of a drawing tube mounted on a stereomicroscope (Leica MZ8).

Taxonomic Account

Philocheras breviflagella Komai, n. sp. Figures 1-3

Material Examined:

Holotype: Ala Moana, O'ahu, Hawai'i, subtidal, 22 December 1999, coll. D. Takaoka, ovigerous female (cl 2.6 mm) (ZRC 2000.0369).

Description:

Body (Figure 1A,B) robust, slightly flattened dorsoventrally. Integument of carapace and abdomen microscopically pitted, with scattered short (curled) or long (plumose) setae.

Rostrum (Figure 1A,B) reaching anterior margin of corneas of eyes, broad, constricted at midlength; anterior margin weakly concave, its width 0.16 of carapace length; dorsal surface deeply concave; lateral margins greatly elevated, unarmed, forming supraorbital eave covering base of ocular peduncle; anterolateral angle rounded; ventral margin weakly concave in lateral view. Carapace (Figure 1A,B) almost as long as wide, slightly broadened posteriorly; median carina extending from anterior 0.4 of carapace, becoming gradually obsolete in posterior 0.2, terminating anteriorly in moderately large gastric spine, dorsal margin weakly sinuous in lateral view; first (dorsolateral) carina extending from anterior 0.2 to near posterolateral margin of carapace, somewhat convergent posteriorly against midline, divided in two sections by wide, shallow notch at about midlength of carina, anterior section distinct, posterior section becoming blunt posteriorly; hepatic carina beginning from anterior 0.14 of carapace, short, rather thick, anteriorly with mesially curved hepatic spine; branchiostegal carina sharp, supporting branchiostegal spine, extending to level of hepatic spine, unarmed; orbital margin strongly elevated; gastric region shallowly depressed on either side of midline; antennal spine showing as broad triangular projection with blunt apex; branchiostegal spine moderately large, reaching anterior margin of cornea of eyes, directed slightly dorsally and mesially; pterygostomian spine small, arising from ventromesial to base...