Thorny Crinoid Crab

Tiaramedon spinosum is a crab species from the Pilumnidae family.

Description

Six spines are prominent on the carapace - two rostral, two epigastric and two lateral branchial. No teeth or lobes on the antero-lateral borders. Carpus and propodus of chelipeds with distal spines.

Carapace squarish, slightly broader than long; regions well defined, protogastric, metagastric, branchial and cardiac regions strongly produced into dorsally directed spines, length of spines varies, protogastric spines always longest; surfaces of carapace smooth, densely covered with short, stiff setae in a systematic fashion. Frontal lobes, triangular, very short, narrow, strongly deflexed downwards, appears beak-like from dorsal view. Inner supraorbital teeth well developed, long, almost 1.5 times longer than broad, produced well beyond and obscuring most of frontal margin. Antero-lateral and postero-lateral margins clearly demarcated; antero-lateral margin sublamelliform, entire, without trace of teeth or lobes; lateral carapace teeth strong, sharp. Antennules folding obliquely, ca. 45° from horizontal, covered with setae; antennular fossae oblique. Surfaces of antenna covered with short stiff setae; antennal free, does not fill orbital hiatus, reaching into orbit; antennal basal segment rectangular; length to width ratio of second antennal segment 1.3-1.8. Eyes well developed, filling orbit; cornea distinct, pigmented; infraorbital tooth distinct, subhepatic tooth distinct. Anterior surface of epistome depressed; posterior margin appears entire because of 2 fused truncate median lobes. Pterygostomial, subhepatic, suborbital regions smooth with occasional scattered, minute granules beneath a dense layer of stiff short setae. Third maxilliped quadrate, surfaces covered with short, stiff setae; ischium rectangular, inner margin mildly granulated, median oblique sulcus shallow; merus squarish; exopod just reaches antero-external edge of merus. Thoracic sternum covered with setae; sutures between sternite segments 1 and 2, 2 and 3 distinct, shallow; between 3 and 4 interrupted medially; lateral clefts indistinct. Abdomen 7 segmented, sutures for all segments visible, all surfaces covered with setae. Chelipeds smooth, densely covered with short, stiff setae; merus and basi-ischium unarmed; carpus with sharp spine on inner distal angle and distinct tooth on outer distal angle; chela stout, length 3 times length of fingers, height ca. 2-3 times height of fingers, distal dorsal margin with distinct elongate tooth; fingers not carinate, pollex not bent downwards. Ambulatory legs unarmed, densely covered with short, stiff setae; meri of all ambulatory legs with strong tooth on subdistal dorsal margin; merus of first ambulatory leg more slender than that of others, unarmed, not cristate; first ambulatory dactylus more elongate and more slender, ca. 1.3 times that on other legs. G1 long, sinuous, tip bends at approximately 90°. G2 relatively short, distal segment short.

Distribution

Western Central Pacific.

Habitat

Lives symbiotic with fetherstars and sea urchins.