Family SEPIADARIIDAE

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Family SEPIADARIIDAE

Bottletail Squids

Compiler and date details

July 2001 - C.C. Lu, National Chung Hsing University, Taichung, Taiwan

Introduction

Members of the Sepiadariidae Fischer, 1882 are small to medium sized sepiolid-like cephalopods. They are benthic dwellers found on the shelf of Indo-west Pacific, Australia and New Zealand (Lu, unpublished data). The genus Sepioloidea with the two described species, S. lineolata and S. pacifica, as well as several other unnamed species are known only from Australia and New Zealand. Sepiadarium with four described species and one undescribed species is found in the Indo-west Pacific northwards to Japan. Four species, S. kochi, S. auritum, S. austrinum and the unnamed species, are found in Australia, the last three species are endemic (Lu, unpublished data).

The first sepiadariid described was Sepiola lineolata Quoy & Gaimard, 1832 (now known as Sepioloidea lineolata) from Jervis Bay, New South Wales (now Australian Capital Territory). d'Orbigny (1839, in Férussac & d'Orbigny 1835–48) recognised it as distinct from Sepiola, and transferred it to a new genus, Sepioloidea. In 1881, Steenstrup erected a new genus Sepiadarium to accommodate his new species S. kochi and grouped Sepiadarium, Idiosepius, Sepiodeidea and Spirula in the family Sepio-Loliginei (Subfamily Sepiadarii). Shortly after, Fischer (1882) created the family Sepiadariidae, restricting it to include only Sepiadarium and Sepioloidea. The first Australian record of a member of Sepiadarium is the description of S. auritum from the Monte Bello Islands by Robson in 1914. Berry (1921) described an additional species S. austrinum, from Gulf St Vincent, South Australia; subsequently, Cotton & Godfrey (1940) recorded S. kochi from South Australia. Recent collecting failed to confirm the latter record and none of Cotton & Godfrey's material can be found in the South Australian Museum, thus their record of S. kochi in South Australia must be regarded as erroneous. However, the presence of S. kochi in tropical northern Australia has been confirmed (Lu & Phillips 1985; Lu, unpublished data).

Eggs and hatchlings of Sepioloidea lineolata were described by Dew (1959). The opaque eggs, white and 10 mm in diameter, were attached individually to rocks by a short stalk. Immediately prior to hatching, one end of the egg began to bulge, the bulge enlarged slightly and with larval movement the bulge finally ruptured and the hatchling shot out, posterior end of the mantle first. Dew (1959) reported that it took 16 days for all the eggs under observation to hatch, indicating that the collected eggs were not of the same age. The young hatchlings, 9–10 mm long and about 4 mm wide, resembled adults in colour and shape. They swam in short jerks for a few minutes after hatching and then settled to the bottom. They were negatively phototropic, and upon settling, proceeded to dig into the sand in the same manner as the adults: with a jerk downwards and forwards and then downwards and backwards. By repeating these movements several times, they quickly disappeared into the sand, leaving only their eyes showing. Sepiadarium austrinum collected from Port Phillip Bay also exhibit this behaviour in the aquarium (Lu, unpublished data). Small amphipods and other small crustacea are the preferred food of the young Sepioloidea lineolata. They stalk and capture their prey in the same way as the adults.

Diagnosis

The body is short and narrow, with ear-like fins that are attached to the lateral sides of the body. The mantle is fused with the head on the dorsal side and with the funnel on the ventral side (in the genus Sepiadarium), or is connected (articulated) with the funnel by a unique locking apparatus (Sepioloidea). The funnel member of the locking apparatus is sole-shaped in outline with a broader deeper anterior pit and a shallower, longer and narrower posterior groove. The mantle cartilage is the complement of the funnel member, consisting of a larger, higher anterior knob and a narrow, lower posterior ridge. The arms are short and are connected by a deep web, particularly around the tentacular base, forming a sac into which the tentacle may retreat. The arms are equipped with two rows of suckers on the proximal part, increasing to four to eight rows distally in some species. In mature males, the left ventral arm is hectocotylised by the disappearance of suckers and transformation of sucker stalks into papillae and small lamellae. The gladius and luminous organs are absent.

In Sepiadarium species, the dorsal mantle surface is covered with large white leucophores surrounded by many smaller red-brownish chromatophores; these are absent in Sepioloidea. The Australian Sepioloidea lineolata has fringed anterior dorso-lateral mantle margins, a feature not seen in other members of the family, in all of which the mantle surface and edges are smooth. Sepioloidea lineolata also differs in having on the dorsal mantle surface a series of longitudinal stripes which, according to Dew (1959), are either blue or more often brown in life, and many round, blunt papillae scattered on the ventral mantle surface particularly towards the edges of the mantle.