Eisothistos anomala (Kensley 1980)

Heteranthura anomala

MATERIAL.—Holotype: USNM 171710, 1 , TL 3.0 mm, Sta JR 33A. Paratype: USNM 171711, 1 juv TL 2.0 mm, Sta JR 29.

DESCRIPTION.—Female: Integument indurate. Body proportions: C > 1 <2 = 3 > 4 > 5 > 6 > 7. Cephalon with eyes situated in broadly rounded anterolateral lobes; rostrum low, rounded. Pereonites 1–6 each with middorsal pit. Pleonites free, 1–5 subequal, 6 with middorsal rounded lobes on posterior margin; each pleonite with prominent plumose seta laterally. Telson broadening distally, indurate, with strong middorsal ridge becoming obsolete distally; distal margin serrate, with few simple and few plumose setae; pair of statocysts situated proximally beneath rounded posterior lobes of pleonite 6.

Antennule elongate-slender, three proximal peduncular segments subequal in length, basal segment broadest, fourth segment one-third length of third; flagellum of six articles, with few aesthetascs distally. Antenna slender-elongate, peduncle 5-segmented, two proximal segments subequal in length, third segment shorter, fourth twice length of third, fifth longer but more slender than fourth; flagellum of four articles. Mouthparts, viewed laterally, elongate and drawn out anterodorsally beyond anterior border of cephalon, beneath shieldlike upper lip. Mandible lacking palp, strongly indurate, armed distally with two strongly sclerotized cusps. Maxilla elongate, indurate, distally strongly curved, armed with one strong and five smaller spines. Maxilliped very elongate-slender, about 14 times longer than wide, 7-segmented, terminal segment tiny, penultimate segment longest. Pereopod 1 unguis half length of dactylus, propodus elongate, palm straight, unarmed except for sensory spine at posterodistal corner. Pereopods 2–4 propodus armed with strong sensory posterodistal spine, and row of about 12 short spines on posterior margin; carpus triangular, unarmed; ischium with six or seven rounded peglike processes. Pereopods 5–7 propodus with strong posterodistal spine, row of about 15 short spines on posterior margin; carpus roughly rectangular, not underriding propodus, with strong posterodistal spine and about 10 short spines on posterior margin. Pleopod 1 exopod and endopod not distinct, fused, forming single plate with slit in distal margin, latter with plumose setae; not strongly indurate, operculiform. Uropodal exopod folding dorsally over telson, bipartite, consisting of elongate, spike-like, basally serrate dorsal section, and rounded ventral part; endopod oval, distally acute, margins serrate, reaching to telsonic apex.

REMARKS—The mouthparts of this species are obviously adopted either to a specialized food or form of feeding. This is seen in the loss of a palp on the strong columnar mandible, which has also lost all trace of a lacinia or molar. The maxilla is also columnar and distally curved toward the midline, with the teeth meeting just below the mandibular cusps. The maxilliped has lost its usual role of ventral shield or plate protecting the mouthparts; it is slender and delicate and, with the few terminal setae it possesses, probably plays only a sensory role in feeding.

The specimens were collected along with some live coral, sponges, and alcyonarians. The unusual mouthparts are probably adapted to feeding on one of these organism types.

ETYMOLOGY.—The specific name is derived from the Greek word anomalos (unusual, abnormal, or inconsistent) and refers to the mouthparts.

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